<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>01.vm.$watch的使用</title>
    <script src="https://cdn.bootcdn.net/ajax/libs/vue/2.6.14/vue.js"></script>
  </head>
  <body>
    <div id="app">{{msg}}</div>
    <script>
      const vm = new Vue({
        el: "#app",
        data: {
          msg: "hello",
          user: {
            name: "jack",
            age: 20,
          },
        },
      });

      // 简单写法
      vm.$watch("msg", function (newValue, oldValue) {
        console.log(newValue, oldValue);
      });

      // 复杂数据类型
      vm.$watch("user", {
        immediate: true,
        deep: true,
        handler(newValue, oldValue) {
          console.log(newValue, oldValue);
        },
      });
    </script>
  </body>
</html>
